1. Field of the invention
The present invention relates to an apparatus and method for measuring an offset of an EPS motor position sensor and, more particularly, an apparatus and method for measuring an offset of an EPS motor position sensor, which can accurately detect an actual rotation angle of the EPS motor by measuring a difference between an actual rotation angle of the EPS motor generated by a mechanical tolerance of the motor position sensor and a value sensed by the motor position sensor.
2. Description of the Prior Art
In general, an Electronic Power Steering (EPS) is mounted on a vehicle so as to easily steer a steering wheel, and an EPS device assists a steering force of a driver using a rotational force of the motor.
The EPS device is provided with an Electronic Control Unit (ECU) that controls the driving of the EPS motor while steering the steering wheel. The ECU receives a signal from a steering angle sensor, a torque sensor, a vehicle speed sensor, and engine rpm sensor, etc., calculates a current value, and provides the calculated current value to the EPS motor so as to control a steering sense of the steering wheel.
As such, when an assistance steering force is controlled by adjusting the current value supplied to the EPS motor, a motor position sensor is used to determine whether the EPS motor is driven at a predetermined rotation angle or a predetermined rotation speed. In general, the motor position sensor is installed on a rotary shaft of the EPS motor in the EPS motor, and senses a rotational speed of the EPS motor by sensing the rotation of a magnet attached to the rotation shaft of the EPS motor.
In order to accurately sense the rotation angle or the rotation speed of the EPS motor, the motor position sensor should be mounted so as to exactly match a center of a rotation shaft of the EPS motor. However, a position difference between the center of the rotation shaft of the EPS motor and a center point of the motor position sensor may occur due to the mechanical tolerance.
Meanwhile, the conventional EPS motor includes a motor position sensor mounted in the EPS motor, and includes a separate EEPROM for storing an offset value for calibrating (correcting) a difference between an actual rotation angle or a rotation speed of the EPS motor and a value sensed by the motor position sensor. Accordingly, the conventional EPS motor has disadvantages in that a cost increases due to the provision of the EEPROM and the size of the EPS motor is large.
To address this problem, it is necessary to propose a method for mounting the motor position sensor to the outside of the EPS motor so as to reduce the size of the EPS motor, and for storing an offset value in an ECU EEPROM that is a memory provided in the ECU, not a separate storage means.
At the same time, as the motor position sensor is mounted on the outside of the EPS motor, it is necessary to develop a method for calibrating/correcting a difference between an actual rotation speed (angle) of the EPS motor, which is distinguished from a conventional case where the motor position sensor is located inside the motor, and a value sensed by the motor position sensor.